While we usually think of butterflies in the spring and summer time, the most amazing aspect of a Monarch butterfly’s life occurs in the fall, when it migrates to a warmer climate for the winter. The fall migration begins as early as August 21, and generally peaks in October. Track the monarch's migration here.

Danaus plexippus is the Monarch’s scientific name. It is an attractive butterfly with orange and black wings, marked along the edge with two rows of white spots, which sometimes spread up to 4 inches wide.

This king of the butterfly world is also called a milkweed butterfly, named for the plant it feeds on. Monarchs are found wherever milkweed plants grow, on all continents except the polar regions. Monarch butterflies appear in particularly large numbers across the northern and eastern parts of the United States as well as in Canada.

Monarch butterflies undergo four metamorphoses (changes in form) during their lifetime – that of an egg, caterpillar (larva), chrysalis (pupa), and butterfly. This entire process takes 4 to 6 weeks.

The female Monarch deposits approximately 400 pinhead-sized yellow eggs on the underside of milkweed leaves. In about a week, a baby caterpillar hatches out of its egg and starts voraciously eating the milkweed. This provides the Monarch with a unique form of protection, because the plant’s milky white juice is both acidic and toxic to many animals. A Monarch caterpillar feeds only on milkweed, absorbing these substances into its body and storing them throughout its life.

The bitter chemicals in the milkweed juices assimilated by the Monarch cause it to become bad-tasting and poisonous. Once a bird has eaten one Monarch caterpillar or butterfly it will never touch another one! So the caterpillar’s conspicuous black, yellow and white stripes and the butterfly’s beautiful orange color serve as a warning symbol to predators.

(Viceroy butterflies look so much like monarchs that birds leave them alone, too. The viceroy is not poisonous and it is good to eat, but the birds don’t know that! Humans can tell the difference because the viceroy is smaller and has an extra black line crossing the veins of the hindwings.)

Monarchs live as caterpillars for a couple of weeks. The caterpillars grow quickly, and to accommodate this rapid growth, the caterpillar sheds its skin (molts) up to five times until it reaches its full length of about two inches - which is up to 2,700 times its original size!

Once it has eaten its fill of milkweed, the caterpillar attaches itself head down to a twig or other sturdy surface. Then it forms a shiny green and gold speckled protective covering around itself, called a chrysalis. This pupal process is completed in a matter of hours.

Packed tightly inside, the caterpillar completes the miraculous process of rebirth by undergoing metamorphosis, in which its tissues and organs transform into a completely different body type. After about 14 days, the chrysalis begins to split open. In this final stage, an adult monarch emerges as a beautiful orange and black butterfly!

The Monarch’s wings are folded and wrinkled, but the butterfly pumps fluid from its abdomen into the wings, which expands them quickly to full size. The Monarch sits for a few hours while waiting for its wings to stiffen and dry before embarking on its maiden flight. A female Monarch has approximately six weeks to seek out nectar, mate, and lay eggs before she dies.

There are usually three generations of monarchs produced each year during the summer. But in late summer and early fall, a special generation of Monarchs is born. These Monarchs live much longer, up to nine months. Triggered by the decreasing daylight and angle of the sun, these butterflies undergo a chemical change delaying maturity, allowing them to migrate south and then remain inactive throughout the winter.

In the spring they will make the long journey back north and lay their eggs on the milkweed plants. When these eggs hatch into caterpillars, the whole cycle starts over again. The next autumn’s offspring will return to the same wintering grounds even though they are several generations removed from those that left the previous fall.

Monarch Migration

The Monarch is unique among butterflies in that it is the only species of butterfly that does not hibernate, but migrates in changing seasons to a temperate climate. In other migrating species, such as birds and whales, the same individuals travel the migration route year after year. In contrast, migrating Monarchs have never been to their destination before. Several generations of Monarchs have lived and died since last year's butterflies departed. So how do they find their way? The butterflies have nothing but instinct to guide them. Scientists think that they may rely on the Earth's magnetic field, the position of the sun, or the polarization of the sun's rays.

Entomologists divide the migrating populations of Monarch butterflies into two groups, one west of the Continental Divide (which is considered too high for the butterflies to fly over), and all of the eastern territory. Monarchs west of the Rockies migrate to the central California coast. (A few Monarchs have even been spotted passing through the Arizona desert!) Monarchs east of the Rocky Mountains spend their winters in the high mountains of central Mexico. Some eastern Monarchs also winter in Florida, along the Gulf Coast of Texas, Cuba and the West Indies.

Monarchs do not fly directly to their final destination in Mexico, but follow a curving route that takes them southward to the vicinity of Georgia and then westward along the Gulf of Mexico. They may go as far as two thousand miles, covering one hundred miles per day, and flying as high as 10,000 feet. Day by day they travel in sun, wind, and rain, across rivers and through forests, winging their way along like migrating birds across the vast continent. Monarchs are able to obtain all of the energy they need from flowers they visit during their journey. Many arrive in good condition despite their long and hazardous flight - a mighty achievement for such a seemingly fragile insect!

When Monarch butterflies are in the north, they are distributed throughout an extensive terrain, but when they migrate south they all stay in the same place. After arriving at their destination, the monarchs cluster in large masses to conserve heat. They rest quietly on the trees, resembling dead leaves, until sunlight warms them enough to fly. On warm days, the butterflies will leave the trees entirely, seeking out nectar sources with which to replenish their energy reserves, but always returning to the trees well before evening.

Monarchs sometimes cover whole trees of eucalyptus and pine groves. Tens of millions of these butterflies spend the winter in a mountain forest of Oyamel fir trees in Central Mexico. Unfortunately, many of the trees that have been homes to these butterflies for years are being cut down, and the Monarch butterfly population is decreasing. But sanctuaries such as the one in Angangueo, Michoacan continue to shelter millions of these gorgeous butterflies.

Did You Know…?

The Aztecs believed in an afterlife where the spirits of their dead would return as butterflies. Images carved in ancient Aztec monuments illustrate this belief in the link between human spirits and the Monarch butterfly. Local inhabitants welcome back the returning butterflies each year, believing that they bear the spirits of their departed. It is these spirits that are honored during Dias de los Muertos, October 31 – November 2.

Butterfly Town USA

Historically, most of North America’s western population of Monarchs - some from as far as the Canadian Rockies and southern Alaska - have migrated to the fog-shrouded Monterey pine forest of Pacific Grove, California. These trees provide the microclimate that they need: proper humidity, light, shade, temperature, and protection from wind. So many Monarchs spend the winter in Pacific Grove that the town is nicknamed “Butterfly Town.”

The number of overwintering Monarchs and the time of their arrival and departure each year varies. As many as 30,000 Monarchs have been counted on Pacific Grove trees. They are fiercely protected by the local citizens, and laws forbid killing or disturbing the visiting butterflies. If you molest a Monarch in Pacific Grove, you will receive a $500 fine!

Each winter, thousands of Monarch butterflies cluster together on the pines and eucalyptus in the Monarch Grove Sanctuary. The Australian eucalyptus trees that were introduced to the area in the 1850's are well-suited to sheltering Monarchs, plus they provide the butterflies with a convenient nectar source since they bloom in winter. Monarchs also cluster in eucalyptus groves at Natural Bridges State Park in Santa Cruz, and at the North Beach Campground in Pismo Beach.

Monarch Butterflies begin arriving in October, and by Thanksgiving most of the Monarchs have settled in. The butterflies attach themselves to trees in huge clusters, and in chilly or damp weather they fold their wings and appear like clumps of dead leaves.

Monarchs are most active from about 10:00 am to 2:00 pm on a sunny day. It is common for them to spread their wings to soak up the sun’s rays and when it’s warm enough, to take flight. This can be quite a beautiful sight! The butterflies don't fly well in temperatures under 55 degrees F.

The Monarchs stay until February or March, when increasing temperatures and longer daylight hours trigger the mating season to take place. By March, most of the butterflies have departed on their spring migration.

Fun Fact: Florida does not have any overwintering sites where Monarch Butterflies congregate in large numbers as they do in Mexico and California, but breeding populations of the butterflies are actively present in the state throughout the winter months.

The Travels of Monarch X, by Ross E. Hutchins. (The true story of a Monarch butterfly that was tagged by a scientist in Canada and captured by a boy in Mexico.Out of print; check your library.)

Monarch and Milkweed, by Helen Frost. (The exacting prose and jewel-toned illustrations echo the harmony of monarch and milkweed in this carefully researched book, explaining one of nature's most spectacular displays in a refreshingly simple manner.)

The Butterfly Alphabet, by Kjell B. Sandved. (Colorful close-up photographs reveal a miniature alphabet in the delicate wing patterns of butterflies and moths from around the world.)

www.monarchwatch.org (This site is dedicated to Monarch butterfly education, conservation, and research, featuring lots of information and links. Learn how to create "waystations" for monarch butterflies, read about the life cycle of the monarch, and more.)

http://www.learner.org/jnorth/monarch (Citizen scientists track the monarch butterfly migration each fall and spring as the monarchs travel to and from Mexico. Report your own observations of migrating butterflies to real-time migration maps. Share data to help scientists understand how monarchs respond to climate and changing seasons. Explore monarch butterfly life cycle, ecology, habitat and conservation needs.)

www.plainfield.k12.in.us/hschool/webq/webq35/monarch1.htm (Webquest: a teacher-led internet activity for the kindergarten level. Learn about the life cycle of a Monarch butterfly, travel from Indiana to Mexico, and visit an actual city in Mexico where Monarchs migrate to in the fall.)

www.adver-net.com/monpics.html (Close-up photos show how to tell the difference between a male and female monarch butterfly. Males may be easily distinguished by the dark spot on their hindwing. Females have thicker black veins and no identifying spot.)